Approach to Vesiculobullous Disorders
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Direct answer
Vesiculobullous disorders are classified by the level at which the skin splits, which separates intraepidermal from subepidermal blistering diseases. Histology locates the split and identifies the inflammatory cells, while direct immunofluorescence shows whether autoantibodies lie between keratinocytes, along the basement membrane or in the dermal papillae. Bedside features such as tense or flaccid bullae and the Nikolsky sign narrow the differential before any test is sent.
What you must remember
- Intraepidermal split: pemphigus shows suprabasal acantholysis with intercellular IgG, unlike the inherited acantholytic disorders.
- Inherited acantholysis: Hailey-Hailey and Darier disease split within the epidermis but have no circulating autoantibodies.
- Subcorneal split: subcorneal pustular dermatosis and the subcorneal type of IgA pemphigus show pustules beneath the stratum corneum.
- Subepidermal with eosinophils: bullous pemphigoid has tense bullae, eosinophils and linear IgG or C3 along the basement membrane.
- Papillary split with neutrophils: dermatitis herpetiformis shows neutrophilic microabscesses and granular IgA in the dermal papillae.
- Anchoring fibril target: epidermolysis bullosa acquisita splits below the lamina densa, with IgG binding the dermal side.
- Bedside clue: the Nikolsky sign is positive in pemphigus, where lateral pressure detaches the epidermis, and negative in pemphigoid.
A grid for sorting blistering diseases
Systematic classification starts with the level of the split and then narrows by inflammatory cells and immunofluorescence. The table places each common disease in its own cell of that grid.
| Disease | Level of split | Histology | Direct IF |
|---|---|---|---|
| Pemphigus vulgaris | Suprabasal, intraepidermal | Acantholysis, tombstone basal cells | Intercellular IgG and C3 |
| Pemphigus foliaceus | Upper epidermis, granular layer | Superficial acantholysis | Intercellular IgG |
| Bullous pemphigoid | Subepidermal, lamina lucida | Subepidermal blister with eosinophils | Linear IgG and C3 at basement membrane |
| Dermatitis herpetiformis | Dermal papillae | Neutrophilic microabscesses in papillae | Granular IgA in papillae |
| Epidermolysis bullosa acquisita | Sublamina densa | Subepidermal split, neutrophils | Linear IgG and C3 at basement membrane |
| Herpes simplex | Intraepidermal, intravesicular | Ballooning, multinucleated giant cells | Negative |
Most exam questions can be answered once the split and the immunofluorescence pattern are known, since each disease occupies a distinct cell of this grid. A useful sequence is to decide the split on histology, check the inflammatory cell, and then read the immunofluorescence. Viral blisters sit in the same grid, separated by a negative immunofluorescence and giant cells on a smear.
Where candidates lose marks
Blistering questions usually reward a fixed sequence of reasoning, from the level of split to the immunofluorescence pattern.
- Trap: diagnosing a tense leg blister in an elderly patient as pemphigus Correct: tense bullae with eosinophils and linear basement membrane IF indicate bullous pemphigoid, and the Nikolsky sign is negative.
- Trap: using the Tzanck smear to separate pemphigus from herpes Correct: acantholytic cells suggest pemphigus, while multinucleated giant cells suggest herpesvirus infection; neither proves the diagnosis alone.
- Trap: submitting only H&E for an autoimmune bulla Correct: direct IF is needed to separate intercellular from linear or granular patterns, which histology alone cannot show.
Frequently asked questions
What does the level of split tell you in a blistering disease?
The level of split shows whether a disease is intraepidermal, as in pemphigus, or subepidermal, as in bullous pemphigoid. This single feature narrows the differential more than any other early step.
Which blistering disease shows granular IgA in the dermal papillae?
Dermatitis herpetiformis shows granular IgA deposits in the dermal papillae on direct immunofluorescence, along with neutrophilic microabscesses on histology. It is associated with coeliac disease and responds to dapsone and a gluten-free diet.
How is Hailey-Hailey disease distinguished from pemphigus vulgaris?
Hailey-Hailey disease is an inherited acantholytic disorder with no circulating autoantibodies, whereas pemphigus vulgaris is caused by IgG autoantibodies. Direct immunofluorescence is negative in Hailey-Hailey disease but shows intercellular IgG in pemphigus vulgaris.
Why is the Nikolsky sign useful in vesiculobullous disorders?
The Nikolsky sign is positive in pemphigus, where lateral pressure separates the superficial epidermis from normal-looking skin. It is typically negative in bullous pemphigoid, which helps narrow the diagnosis at the bedside.
When is direct immunofluorescence preferred over histology alone?
Direct immunofluorescence is preferred for autoimmune blistering diseases because it reveals the antibody pattern, which histology alone cannot show. The perilesional biopsy for immunofluorescence should be sent in transport medium rather than formalin.